In order to analyze the mechanism for complex formation, transportation, and secretion of Japanese encephalitis virus glycoproteins (prM and E) during virion morphogenesis, these proteins were expressed in COS7 cells with pcDL-SRalpha transient expression vector system and the region necessary for these functions was analysed using several mutants of prM and E.When C-terminal 4 amino acids deletion mutants of prM was expressed with E protein, E and prM was synthesised in cells, but secretion was strongly inhibited. One to three deletion mutants from C-terminal of prM showed same as wild type prM protein. 11 to 20 amino acids deletion from C-terminal of prM caused low stability of prM and complex of prM and E was decreased. 63 amino acids deletion mutants from C-terminal of prM did not make stable complex with E protein. Tyrosine residue at 51th and 78th of piM are highly conserved during flaviviruses. When these tyrosine residues were changed to leucine residue, prM and E were synthesised in cells but complex of prM and E was not formed and secretion of these proteins was strongly inhibited. These observation shows that for complex formation and transportation of prM and E, both C-terminal region and N-terminal structure of prM is important.